(1) Field of the Invention
The present invention pertains to a protective cover for a lamp and in particular to a reusable color filter that can be removably attached to the mounting assembly of a halogen lamp used in an emergency warning light to protect the lamp and change the color of the light emitted by the lamp while providing a flow of air to cool the lamp.
(2) Description of the Related Art
From 1915 to 1950, virtually all emergency warning lights were devices that incorporated an incandescent lamp and a parabolic reflector, both mounted behind an essentially flat color glass filter. The reflector directed light emitted from the lamp through the colored glass filter. The flashing of the light was produced by interrupting the current to the lamp. Although these devices were simple and inexpensive, they were considered to have two serious deficiencies.
First, the emergency warning lights were highly directional and projected a flash of warning light in only a fraction of the perimeter around the vehicle on which the warning light was mounted. Second, because it was necessary to reheat the lamp filament at the start of each flash, the warning lights were very inefficient.
In the late 1940""s, the rotating beacon warning light was developed. The rotating beacon also used an incandescent lamp and a parabolic reflector positioned behind the lamp. However, flashes of the lamp were obtained by using a small motor to rotate the lamp and reflector together inside a colored, circular lens. Although the rotating beacon warning light eliminated the previous directional deficiencies of warning lights, using the same single light source as the previous directional warning light (typically a 30-60 watt bulb), the 360xc2x0 signal emanating from the rotating beacon was not nearly as intense as that generated by the older directional devices that concentrated their energy in an arc of about 30xc2x0.
To overcome the shortcomings of the rotating beacon signal light, a sealed beam spotlight lamp was used in place of the bulb and reflector. By using as many as 4 sealed beam spotlight lamps mounted on a common turntable, acceptable levels of warning light flashes were achieved in all directions around the vehicle on which the rotating sealed beam spotlight lamp warning light was mounted.
Whether a directional warning light, a single lamp rotating or multiple lamps rotating warning light, all warning lights typically used a colored lens to produce a light signal of a single color. For a few special applications, two lenses were cut in half and glued together to form a split lens that, for example, flashed red to the front and yellow to the rear.
After the introduction of the multiple sealed beam spotlight lamp beacon, they were modified by putting colored faces on the spotlight lamps and enclosing the multiple spotlight lamps inside a clear lens. Combinations of red and clear colored faces on the spotlight lamps were also used. However, the sealed beam spotlight lamps were disadvantaged in that they were expensive and relatively heavy. They required large and expensive motors and turntables to support and rotate the spotlight lamps. In addition, it was noticed that in those signal lights employing colored faces on the spotlight lamps that the colors were not very heat resistant and would burn away.
In the mid-1970""s, the lightbar emergency warning light was introduced. Basically, the lightbar was constructed of a series of rotating spotlight beacons mounted in a row under rectangular lenses. However, it was soon discovered by police departments that their cars equipped with lightbars using colored lenses could be seen for miles, even when the warning lights were off. Cars using lightbars with clear lenses over colored sealed beam lamps were equally effective with their lights on, but were much less visible with their lights off.
Halogen headlights using replaceable halogen capsules were introduced in the 1980""s and soon ended the use of conventional sealed beam lamps for headlights. By using the same inexpensive halogen capsule, warning light manufacturers realized they could produce a less expensive but higher performance product. However, the halogen lamp could not be used with the conventional clear lenses. The halogen lamps burn very hot and required envelopes of special glass and it was found to be impractical to color the glass as was done for sealed beam spotlight lamps.
To overcome this problem, several filter designs were developed, such as that disclosed in U.S. Pat. No. 4,543,622. The filter design of this patent was successful when used with 360xc2x0 rotating light elements and is still widely used. With rotating signal light elements, the common method for obtaining color signals from a halogen lamp under a clear lens is to attach a filter to the reflector of the signal light element so that it rotates with the reflector. However, when this is attempted with an oscillating signal light having an oscillating reflector of the type described in U.S. Pat. No. 5,385,062; U.S. Pat. No. 5,697,691; U.S. Pat. No. 5,842,768 and U.S. Pat. No. 5,676,447, the filter adds substantial weight to the light element and changes the arc of coverage of the warning light signal.
Colored halogen warning signal lamps have been designed that have a close fitting colored glass tube positioned over the halogen bulb. One end of the colored glass tube is closed and the other end is open. A standard halogen lamp is inserted into the tube and a high temperature cement is used to permanently bond the open end of the colored glass filter tube to the metallic base of the halogen lamp. However, the close fitting glass tube appreciably increases the operating temperature of the halogen lamp. These lamps with colored tubes were primarily designed for use in a current interrupted flashing warning light with less than a 50% duty cycle. It was found when these lamps were used in a 100% duty cycle device, such as a rotating or oscillating beacon, the halogen lamp life was less than half of that obtained when the halogen lamp is operated without the colored filter. The addition of the close fitting, closed filter increases the internal temperature of the halogen bulb and leads to its rapid failure. In addition, the manufacture of a halogen lamp with a permanent color filter secured over the lamp bulb significantly increases the price of the halogen lamp alone. With less than half of the useful life of the halogen lamp at a significant increase in cost over the halogen lamp, the use of the halogen lamp with the colored filtered tube was considered too impractical for use in continuous duty warning lights.
What is needed to overcome the shortcomings experienced in providing color to a signal light produced by a halogen lamp in an oscillating or rotating signal light assembly under a clear lens is a high temperature, colored filter that does not affect the performance of either the halogen lamp or the signal light assembly. The filter should be easily removable from the standard halogen lamp to permit reuse whenever the halogen lamp is replaced.
The present invention overcomes the disadvantages of the prior art by providing a reusable cover assembly that attaches to a standard halogen lamp or any other high temperature light source having a socket and a lamp in the socket. The cover assembly preferably changes a color of light emitted by the lamp while providing a sufficient flow of cooling air through the reusable cover assembly to minimize any reduction in the operating life of the lamp. The reusable cover assembly of the invention does not impede the operation of the oscillating or rotating element or require expensive segmented lenses around the oscillating element. The cover assembly not only filters light emitted by the lamp, but also functions as a protective cover over the lamp that protects the lamp from accidental contact.
The reusable cover assembly of the present invention includes a metallic connector that attaches to the lamp or lamp socket of a signal light assembly and a cover in the form of a high temperature colored filter that surrounds the lamp. The connector easily snaps over a standard halogen lamp and lamp socket and holds the reusable cover assembly securely to the signal light assembly. The connector permits easy removal of the cover assembly from the signal light assembly when the lamp burns out and allows easy installation of the reusable cover assembly over a replacement lamp.
The connector of the cover assembly has a filter or cover mounting portion that is connected to a lamp or lamp socket mounting portion. The lamp or lamp socket mounting portion attaches to the lamp or lamp socket of the signal light assembly and the cover mounting portion supports the colored filter over the signal light lamp. The connection between the filter or cover mounting portion of the connector and the colored filter or cover is flexible to compensate for the differences in the coefficient of thermal expansion between the filter and the filter mounting portion of the connector. Because the connection between the connector and filter is subjected to a wide range of temperatures as the lamp is switched from a de-energized state to a prolonged operating state, the flexible connection between the connector and filter ensures the integrity of the cover assembly.
The metallic connector has an arrangement of vent openings that permit entry of cooling air into the cover assembly and between the colored filter lamp cover and the lamp. The filter cover is provided with a top vent hole to permit exiting of air heated by the lamp from inside the cover. Cooling air enters through the arrangement of vent openings in the cover assembly, flows between an interior space between the lamp and the filter cover thereby cooling the lamp to keep it operating properly for a longer period of time, and then escapes through the top vent hole of the filter cover. The top of the colored filter cover or the area of the cover around the top vent hole is preferably rounded and/or tapered to minimize the passage of unfiltered white light from the lamp through the vent hole.
The reusable cover assembly of the present invention provides colored light for a warning signal light yet does not appreciably affect the performance of the halogen lamp or the oscillation means by which the signal light assembly is rotated or oscillated through an arc. The reusable cover assembly of the invention is easily removable from the lamp or lamp socket of the standard signal light assembly and permits reuse whenever the halogen lamp is replaced. In addition to providing a colored filter for the halogen lamp, the cover assembly also protects the lamp from accidental contact.